Usage and Examples for dhcputils (encode)¶

The DHCP Utils provides classes to assist with the encoding and decoding of DHCP options in to/from hexidecimal. The primary use case is for sub-option encoding for custom option spaces, in particular, Option 43 encoding.

Encoding Class¶

The bloxone.dhcp_encode() class provides a set of encode methods to enable the encoding of defined DHCP sub options and data.

To encode the specific data-types a set of type_to_hex methods are provided. These will take a specific input data=type and apply the required encoding methodology to generate a compliant hexidecimal string for

Usage¶

The core aim of the class is to provide a simpler interface to encode DHCP sub options defined as a dictionary and provide an encoding.

To ensure flexibility the encoding is broken down in to three methods: encode_dhcp_option(), encode_sub_option() and encode_data().

Sub-options are defined as a dictionary, with three required keys:

‘code’

the sub option code

‘type’

the data-type

‘data’

the data to encode using the specified type

And several optional keys:

‘array’

Boolean to indicate whether the data should be encoded as an array, e.g. array of IP addresses

‘data-only’

Boolen to indicate that only the data in the sub option should be encoded. i.e. do not add the encoded option code and length

For example:

sub1 = { 'code': 1, 'type': 'string', 'data': 'ABCDEFG'}
sub2 = { 'code': 2, 'type': 'ipv4_address',
         'data': '10.10.10.10,10.11.11.11', 'array': True }

Since there is typically more that one sub-option required, these can be added to a list that is processed, and encoded, by the encode_dhcp_option() method:

options = [ sub1, sub2 ]

An example, with example output is shown below:

import bloxone

de = bloxone.dhcp_encode()

# Set up the sub-options
sub1 = { 'code': 1, 'type': 'string', 'data': 'ABCDEFG'}
sub2 = { 'code': 2, 'type': 'ipv4_address',
         'data': '10.10.10.10,10.11.11.11', 'array': True }

# Create list for option to be encoded together
options = [ sub1, sub2 ]

# Encode e.g. for Option 43
h = de.encode_dhcp_option(options)
print(h)

'''
>>> print(h)
01074142434445464702080a0a0a0a0a0b0b0b
'''

# Show the encoding for just one sub-option
print(de.encode_sub_option(sub2))

'''
>>> print(de.encode_sub_option(sub2))
02080a0a0a0a0a0b0b0b
'''

test_data = { 'code': '101', 'type': 'fqdn', 'data': 'www.example.com' }
hex_data = encode_data(test_data)

'''
>>> print(de.encode_data(test_data))
03777777076578616d706c6503636f6d00
'''

Return a list of supported data types:

>>> import bloxone
>>> de = bloxone.dhcp_encode()
>>> de.opt_types
['string', 'ipv4_address', 'ipv6_address', 'boolean', 'int8', 'uint8',
 'int16', 'uint16', 'int32', 'uint32', 'fqdn', 'binary', 'empty']

Each of the supported data-types has a specific method of the format type_to_hex(). These can be directly access and typically support data both in its native format and as a string:

de.string_to_hex('Hello World')
de.ip4_address_to_hex('192.168.1.101')
de.fqdn_to_hex('www.infoblox.com')
de.int8_to_hex('22') or int8_to_hex(22)

etc

Specific functions to return the length of the hexidecimal string in hex and encoding of the option code (basically a wrapper of int8), are also provided:

h = de.ip4_address_to_hex('10.10.10.10')
de.hex_length(h)
de.optcode_to_hex(125)

A tests() method is also provided that will show example encodings for each data-type and option encodings:

>>>de.tests()
Encoding types supported: ['string', 'ipv4_address', 'ipv6_address', 'boolean', 'int8', 'uint8', 'int16', 'uint16', 'int32', 'uint32', 'fqdn', 'binary', 'empty']

Non-array tests:
Type: string: AABBDDCCEEDD-aabbccddeeff, Encoded: 4141424244444343454544442d616162626363646465656666, Length(hex): 19
Type: ipv4_address: 10.10.10.10, Encoded: 0a0a0a0a, Length(hex): 04
Type: ipv4_address: 10.10.10.10,11.11.11.11, Encoded: 0a0a0a0a0b0b0b0b, Length(hex): 08
Type: boolean: True, Encoded: 01, Length(hex): 01
Type: int8: 22, Encoded: 16, Length(hex): 01
Type: int8: -22, Encoded: 96, Length(hex): 01
Type: uint8: 22, Encoded: 116, Length(hex): 01
Type: int16: 33, Encoded: 0021, Length(hex): 02
Type: int16: 33, Encoded: 0021, Length(hex): 02
Type: uint16: 33, Encoded: 10021, Length(hex): 02
Type: int32: 44, Encoded: 0000002c, Length(hex): 04
Type: uint32: -44, Encoded: ffffffd4, Length(hex): 04
Type: uint32: 44, Encoded: 10000002c, Length(hex): 04
Type: fqdn: www.infoblox.com, Encoded: 0377777708696e666f626c6f7803636f6d00, Length(hex): 12
Type: binary: DEADBEEF, Encoded: deadbeef, Length(hex): 04
Type: empty: , Encoded: , Length(hex): 00
Type: ipv6_address: 2001:DB8::1, Encoded: 20010db8000000000000000000000001, Length(hex): 10
Type: ipv6_address: 2001:DB8::1,2001:DB8::2, Encoded: 20010db800000000000000000000000120010db8000000000000000000000002, Length(hex): 20

Padding test (1 byte), type string: AABBCCDD 414142424343444400
Full encoding of sample: 01194141424244444343454544442d61616262636364646565666602040a0a0a0a03080a0a0a0a0b0b0b0b040101050116
>>>